Coexistence refers to the ability for multiple wireless protocols to operate in or around the same or adjacent time-frequency radio resources without significant degradation to any radio's operation due to interference. Note that interference may occur at a reception radio frequency or at any intermediate frequency used within a receiving device for the purpose of demodulation. Without coexistence mechanisms, radio frequency interference can cause, amongst other degradations, loss of connectivity, decreased data throughput or reduction in quality of service, or increased current drain.
When adjacent radio frequency bands are allocated to different uses, wireless interference can result. In general, there is an elevated risk of wireless interference when a frequency band used for uplink transmissions is adjacent to a frequency band used for downlink transmissions; the wireless transmissions in one band can create interference for wireless receivers operating in the adjacent band.
For example, a user equipment (UE) transmitting at 704-716 MHz (e.g., the United States Federal Communication Commission Lower 700 MHz band, B and C blocks) can interfere with nearby or collocated user equipment receiving at 716-728 MHz (e.g., the United States Federal Communication Commission Lower 700 MHz band, D and E blocks). As another example, a base station (eNB) transmitting at 734-746 MHz (e.g., the United States Federal Communication Commission Lower 700 MHz band, B and C blocks) can interfere with a nearby or co-sited base station receiving at 716-728 MHz (e.g., the United States Federal Communication Commission Lower 700 MHz band, D and E blocks).
The United States (US) Federal Communication Commission (FCC) established common emission spectrum limits and common field strength limits for this entire section of spectrum (i.e., 698-746 MHz). Given these limits, a common method applied to alleviate interference is to introduce a “null” or “guard” frequency band between deployed bands that are sufficient to reduce or avoid interference. However, there is very little guard (nominally zero) band between the US FCC Lower 700 MHz C block (710-716 MHz) and its adjacent Lower 700 MHz D block (716-722 MHz).
As guard bands narrow, improved filtering and/or physical separation of transmit and receive antennas is commonly used to reduce interference caused by adjacent channel leakage (such as harmonics, intermodulation components, parasitic emissions, frequency conversion spurious emissions, etc.). Although this is feasible at base stations, improved filtering and antenna separation may be difficult or prohibitively expensive to implement in user equipment where physical constraints (such as small dimensions which result in low coupling losses between transmitting and receiving antennas) and low cost targets apply. Because multiple radios can wirelessly interfere with each other in various ways, and effective filtering may not be available at a reasonable cost, coexistence mechanisms should be developed for a variety of collocated and non-collocated scenarios.
With the continuing emergence of a variety of wireless communication technologies operating in adjacent frequencies, there is an opportunity to provide more effective solutions to mitigate interference and coexistence problems among collocated and non-collocated radios. The various aspects, features and advantages of the disclosure will become more fully apparent to those having ordinary skill in the art upon careful consideration of the following Drawings and accompanying Detailed Description.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments. Also, flowchart boxes may be rearranged into different sequential orders, repeated, or skipped in certain instances.
The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.